DETERMINATION OF HEAVY METALS IN SOME SELECTED VEGETABLES IRRIGATED WITH POLLUTED WATER IN KABALA WEST AREA OF KADUNA STATE

DETERMINATION OF HEAVY METALS IN SOME SELECTED VEGETABLES IRRIGATED WITH POLLUTED WATER IN KABALA WEST AREA OF KADUNA STATE

ABSTRACT

This study was carried out to assess the levels of different heavy metals such as Lead, Cadmium and Zinc in Vegetables like cabbage, lettuce, spinach, Bitter leaf and pumpkin irrigated with polluted water in different farms in Kabala West area of Kaduna state, the concentrations of the heavy metals were determined using Atomic absorption spectrophotometric analysis, the result shows that lead (2.130-9.075 mg/kg), Cadmium (1.365-1.735 mg/kg) and Zinc (2.720-6.765 mg/kg) were detected in all the samples except for Zinc which was not detected in lettuce and cabbage. The concentration of lead (9.075 mg/kg) detected in spinach was the highest and that of cadmium (1.365 mg/kg) detected in bitter-leaf was the lowest in all the samples analyzed. The result also indicated that Lead and cadmium detected in all the samples analyzed in this project were above the permissible limit of (0.3 mg/kg) and (0.10 mg/kg) respectively with the exception of Zinc which was below the permissible limit of (100 mg/kg) set by FAO/WHO in 2001.

CHAPTER ONE

1.0     INTRODUCTION

The consumption of vegetables as food offer rapid and least means of providing adequate vitamins, supply minerals and fibers. Vegetables that are used as food include those used in making soups or served as integral parts of the main sources of a meal. Leafy vegetables occupy a very important place in the human diet (Zurera et al., 1999), but unfortunately constitute a group of food which contributes maximally to nitrate and other anions as well as heavy metal consumption. Heavy metals deposition are associated with a wide range of sources such as small scale industries (including battery, Metal smelting and cable coating industries); vehicular emissions, and diesel generator sets. Heavy metals such as cadmium, lead and zinc are important environmental pollutant, particularly in areas where vegetables are irrigated with waste water, consumption of vegetables such as spinach, cabbage, lettuce, Bitter leaf and pumpkin by humans and animals pose serious health hazards, Although some heavy metals as Lead, Cadmium and Magnesium are important in plant nutrition,   many of them do not play any significant role in the plant’s physiology. The uptake of these heavy metals especially into the human food chain is done through these leafy vegetables and they have harmful effects on health (Jarup, 2003).

Vegetables act as neutralizing agents for acidic substances formed during digestion, as human activities increases especially with the application of modern technology, pollution and contamination of human food chain has become inevitable. Heavy metals cannot be underestimated as these food stuffs are important components of human diet, they are very rich and comparatively cheaper sources of vitamins, Consumption of these items provides taste and palatability increases appetite and provides fibre for digestion and prevent constipation (Agrawal, 2011). Heavy metal contamination of food item is one of the most important aspect of food quality assurance; International and national regulation on food qualities have lowered the maximum permissible levels of toxic metals in food items due to an increased awareness of the risk these metals pose to food chain contamination.

Rapid and Unorganized industrialization and   Urbanization has contributed to the elevated levels of metals in the urban environment in developing countries, Heavy metal are non bio- degradable and persistent environmental contaminants which may deposited on the surfaces and then absorbed into the tissues of the vegetables; Plants take up heavy metals by absorbing them from deposits on the parts of the plant exposed to the polluted water (Amoah, 2008) Waste water from industries of mining electroplating paints or chemical laboratories often contains high concentrations of heavy metals, These elements at concentration exceeding the physiological demand of vegetables, not only could administer toxic effects in them but also could enter food chain, get biomagnified and pose a potential threat to human health. Heavy metal contamination in agricultural soils from waste water irrigation is of serious concern due to its implications on human health.

1.1            EFFECTS OF HEAVY METALS ON HUMAN HEALTH

Small amounts of heavy metals are needed in our environment and diet and are actually necessary for good health, but large amount of any of them may cause acute or chronic toxicity (poisoning). Heavy metal toxicity can result in damaged or reduced mental and central nervous function, lower energy levels and damage to blood composition, lungs, kidneys, liver, and other vital organs. Long term exposure may result in slowly progressing physical, muscular, and neurological degenerative processes, allergies are not uncommon, and repeated long-term contact with some metals (or their compounds) may cause cancer (WHO, 2006). For some heavy metals, toxic levels can be just above the background concentrations naturally found in nature. Therefore, it is important to learn about heavy metals and take protective measures against excessive exposure. The association of symptoms indicative of acute toxicity is not difficult to recognize because they are usually severe, rapid in onset, and associated with a known ingestion or exposure. Symptoms include: cramping, nausea and vomiting; pain; sweating; headache difficulty in breathing impaired cognitive motor, and language skills, mania and convulsions symptoms of chronic exposure (impaired cognitive and language skills, learning difficulties; nervousness and emotional instability; and insomnia, nausea, lethargy, and feeling ill) are also usually recognized; however, they are much more difficult to associate with their cause(Jarup, 2003). Symptoms resulting from chronic exposure are very similar to symptoms of other health conditions and often develop slowly over mouths or even years. Sometimes, symptoms of chronic exposure subside; thinking the symptoms are related to something else people postpone seeking treatment. (Khillare et al., 2004).

  

1.2            BENEFITS OF HEAVY METALS

In small quantities, certain heavy metals are nutritionally essential for a healthy life. Those elements, or some form of them, fruits and vegetables and in commercially available multivitamin products (WHO, 2006), this research work focuses on vegetables because it is widely consumed in Nigeria, so it is important to know about their relationship with heavy metals. Diagnostic medical application include direct injection of gallium during radio logical procedures dosing with chromium in parent nutrition mixtures, and the use of lead as x-ray shield (Jassir, M.S., et al , 2005). Heavy metals are also common in industrial applications such as the manufacture of pesticides, batteries, alloys, electroplated metal parts, textile dyes, steel, and so forth (WHO, 2006). Many of these products are in our homes and add to the quality of life when properly used.  

1.3            AIMS AND OBJECTIVES

         The aim of this project work is to determine heavy metals in some selected vegetables in Kabala West, Kaduna, Nigeria..

Objectives

·                    The objective of this work is to ascertain the level of heavy metals in analyzed samples

·                    To determine the concentration of heavy metals in the selected vegetables

1.4            SCOPE OF WORK

The scope of this project work covers the determination of the presence of heavy metals in vegetables grown in kabala west area of Kaduna state, and also to determine the various concentrations of the heavy metals in the selected vegetables.

JUSTIFICATION

         Previous projects have been carried out to ascertain different levels of heavy metals in soil and water samples, but this project specifically targets heavy metals in vegetables grown and irrigated with polluted water in Kabala area of Kaduna state.

CHAPTER TWO

2.0     LITERATURE REVIEW

Heavy metals are members of a loosely defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinide. Heavy metals occur naturally in the ecosystem with large variations in concentration (Mohsen and Salisu , 2008) they are metallic elements that are toxic and has high density, specific gravity or atomic weight, metals with a potential negative health effect or environmental impact may be termed heavy metals (Kabata and Pendias, 1999). There are over 50 elements that can be classified as heavy metals, but only 17 that are considered to be both very toxic and relatively accessible. Lead, zinc, cadmium, magnesium and cobalt should be given particular attention, in terms of water pollution. Toxicity levels depend on the type of metal, its biological role, and types of organism that are exposed to it, toxic metals are often added to the streams as salt (sulfides, phosphate and carbonates), are very insoluble in hard water and usually travel with sediment. The transformation into readily accessible materials is a complex process and depends on many factors such as pH, sediment presence and hardness. The availability of these metals is determined by precipitation-dissolution reactions which are strongly affected by pH. Therefore at lower pH, heavy metals are more available and more reactive. Many of these metals then undergo Methylation, as a result of bioaccumulation where bacteria absorb these elements and convert them from a metallic state into a toxic organ metallic state. By becoming incorporated with an organic component, these metals become readily available to the first tropic level of the food chain and eventually lead to biological magnification throughout the system (Laura and Susan, 2009).

2.1     EXAMPLES OF HEAVY METALS

2.1.1  LEAD

Lead is a chemical element in the carbon group with symbol Pb (from Latin Plumbum) and atomic number 82, Lead is a soft and malleable metal, which is regarded as a heavy metal and poor metal. Metallic lead has a bluish-white colour after being freshly cut, but it soon tarnish to a shiny chrome-silver luster when it is melted into a liquid. Lead is a p-block element in period 6 and group 4, it has a standard atomic weight of 207.2, lead has a melting point of 327.46⁰c and a boiling point of 1749^oc. lead, at certain contact degrees, is a poisonous substance to animals, including humans. It damages the nervous system and cause brain disorders. Excessive lead also causes blood disorders in mammals; lead is a neurotoxin that accumulates both in soft tissues and bones. Lead has high density, softness, ductility and malleability, poor electrical conductivity compared to other metals, high resistance to corrosion, and ability to react with organic chemicals. Lead is classified as a post transition metal and is also a member of the carbon group. Lead only forms a protective oxide layer although finely powdered, highly purified lead can ignite in air. Melted lead is oxidized in air to lead monoxide (Torabian and Mahjouri, 2002). Lead has electronic configuration of 1S² 2S² 2P⁶, 3S², 3P⁶,  4S², 3d¹⁰, 4P⁶, 5S², 4d¹⁰, 5P⁶, 6S², 4F¹⁴, 5d¹⁰, 6P²   

2.1.2  ZINC

Zinc is a metallic element that has a symbol of Zn and atomic number 30. It is the first element in group 12 of the periodic table, Zinc is in some respects chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2. Zinc is the 24^th most abundant element in the earth’s crust and has (5) five stable isotopes. Zinc has a standard atomic weight of 6.538 and an electronic configuration of 1S², 2S², 2P⁶, 3S², 3P⁶, 4S², 3d¹⁰ Zinc has a density of 7.14g.cm^-3 with a melting point of 419.53⁰C and a boiling point 907⁰C.

Zinc is an essential mineral of exceptional biological and public health importance.

 Zinc deficiency affects about two billion people in developing world and is associated with many diseases, in children it causes growth retardation, delayed sexual maturation, infection susceptibility and diarrhea, contributing to the death of about 800,000 children word wide per year (Obuobie et al., 2006).

Zinc is also referred to in nonscientific context as spelter, is a bluish white lustrous, diamagnetic metal, the metal is hard and brittle at most temperatures but becomes malleable between 100 and 150⁰C

2.1.3  CADMIUM

Cadmium is a chemical element with the symbol Cd and atomic number 48. This is a soft, bluish-white metal and is chemically similar to the two other stable metals in group 12 of the periodic table, zinc and mercury. The average concentration of cadmium in earth’s crust is between 0.1 and 0.5 parts per million. Cadmium is an impurity of Zinc ore, Zinc has a density of 8.65 g.cm^-3, a melting point of 321.07⁰c and a boiling point of 767⁰C (Pescod, 1999). Cadmium has many common industrial uses as it is a key component in battery production, cadmium pigment coatings is also used in electroplating.

Cadmium electroplating consuming 6% of the global production can be found in the aircraft industry due to the ability to resist corrosion when applied to steel component (Pilot and Dragan, 1996), Cadmium has an electronic configuration of 1S²2S²2P⁶3S²3P⁶4S²3d¹⁰4P⁶5S²4d¹⁰

2.2     VEGETABLES

In culinary terms, a vegetable is an edible plant or its part, intended for cooking or eating raw, vegetables are most often consumed as salads or cooked in savory or salty dishes, while culinary fruits are usually sweet and used for desserts. Some vegetables can be eaten raw, some cooked, and some must be cooked to destroy certain natural toxins or microbes in order to be edible (Thompson and Kelly, 2003). Below are some examples of vegetables

2.2.1  LETTUCE

Lettuce (Lactuca Sativa) is an annual plant of the aster or sunflower family Asteraceae. It is most often grown as leaf vegetables, but sometimes for its seed and stems, lettuce is easily cultivated, although it requires relatively low temperature to prevent it from flowering quickly. Lettuce grows in full sun in loose nitrogen rich soils with a pH of between 6.0 and 6.8 (Radwan and salama, 2006).

2.2.2  CABBAGE             

Cabbage is a leafy green plant, grown as an annual vegetable for its dense-leave heads, closely related to other Cole crops, such as broccoli, cauliflower cabbage heads generally range from 1- 8 pounds (0.5 to 4 kg)and can be green purple and white.

It is difficult to trace the history of cabbage, but it was most likely domesticated somewhere in Europe before 1000 BC. Cabbage seedlings have a thin taproot and have hard shaped cotyledons. The first leaves produced are ovate (egg-shaped) (Pendias and John, 2002).

2.2.3  FLUTED PUMPKIN

          Fluted pumpkin (Telfairia Occidentalis) is a tropical vine grown in West Africa as a leaf vegetable and for its edible seeds. Common names for the plant include fluted gourd, and Ugu. The plant is drought tolerant, dioeciously perennial,

The young shoots and leaves of female plants are the main ingredient of a Nigerian meal, Ofe Egwusi. The large (up to 5cm), dark-red seed is rich in fat and protein and can be eaten whole, ground into powder for another kind of soup or made into fermented porridge. It is propagated using the seeds. Its seed is housed in another greater covering or hard shell which protects it from harm, it survives drought and can retain its life in the root even after many years, It is a creeping plants and grows well if staked with bamboo sticks, the fruit of the plant is large and can weigh up to 13 kg and is inedible (yargholi and Azimi, 2008).

2.24   BITTER-LEAF

Vernonia Amygdalina also known as bitter leaf is a member of the Asteraceae family, is a small shrub that grows in tropical Africa, it grows typically to a to a height of  2 – 5m. The leaves are elliptical and up to 20 cm long. Its bark is rough,  It is commonly called bitter leaf in English because of its bitter taste. Some Nigerian common names given to this plant include ewuro (Yoruba), onugbu (Igbo), tyuna (Tiv), oriwo (Edo) and chisar-doki in Hausa (Angelova et al., 2004).

The leaves may be eaten either as a vegetable (macerated leaves in soups) or aqueous extracts as tonics for various illnesses. Vernonia Amygdalina extracts and isolated chemical constituents have been studied for their potential pharmacological effects (Ayers and westcot, 2001).

2.2.5  SPINACH

Spinach (Spinacia Oleracea) is an edible flowering plant in the family of Amaranthaceae. It is native to central and south western Asia. It is an annual plant (rarely biennial), It grows to a height of up to 30 cm. the leaves are alternatie, simples, ovate to triangular based, very variable in size from about 2-30cm long and 1-15cm broad, with larger leaves higher on the flowering stem. The flowers are inconspicuous, yellow­-green, 3-4mm diameter, maturing into a small, hard, dry, lumpy fruit cluster 5-10mm across containing several seeds (Bigdelli and Sielspour, 2008). It is super-cold-handy vegetable and it is a tender crop. Spinach has similar growing conditions and requirements as lettuce, but it is more versatile in both its nutrition and its ability to be eaten raw or cooked. It is higher in iron. Calcium and vitamins than most cultivated green and one of the best sources of vitamins A, B and C (Haiyan and Stuanes, 2003).

CHAPTER THREE

3.00   MATERIALS AND METHODS

3.1.0  EXPERIMENTAL MATERIALS

The instruments and reagents used in this project were of analytical grade, these materials include:

a.                 Beaker 100cm³

b.                 Conical flask 100cm³

c.                  Crucible

d.                 Funnel

e.                  Whattman No.1 filter paper

f.                   Measuring cylinder 50cm³

g.                 Weighing balance (DS-75)

h.                 Distilled water

i.                   Digestion flask 50cm³

j.                   AAS spectrophotometer (PG-990)

k.                 Perchloric acid (HCl0₄)

l.                   Nitric acid (HN0₃)

m.              Concentrated sulphuric acid (H₂S0₄)

3.2.0  METHOD

3.2.1  SAMPLES

Some commonly consumed vegetable were used as samples for the analysis of the heavy metals, they include: Lettuce, Spinach, Fluted- pumpkin, Cabbage and Bitter leaf.

3.2.2 SAMPLE COLLECTION

Three samples each of the 5 vegetable samples were collected randomly from 3 different farms in the outskirts of Kabala west, Kaduna State. Sample of the same vegetables were mixed together to get a representative sample of the vegetable.  Precautionary measures were taken to avoid any form of contamination. After the collection of samples, Digestion followed.

3.2.3    DIGESTION

Digestion is the process of combusting volatile materials in the sample. The volatile materials are usually organic materials such as carbohydrates, fats and oil, protein and other materials.

          After the digestion, it is the inorganic materials usually the trace metal elements that remain. The digestion procedure can be done by two broad methods

(i)    Dry  Ashing

(ii)  Wet Ashing (Milacic and Kralj, 2003).

3.2.3.1 DRY ASHING

          This method involves the complete combustion of all the organic matter only in the raw and processed sample to remain only the non-volatile inorganic mineral element.

The combustion starts by burning the material on the non-luminous part of the Bunsen lame until it stops smoking and then transferred into a muffle furnace which is set between 450⁰ - 550⁰ c (Jarup, 2003). 

However precaution must be taken against low result which may be due to any of the following reasons.

                             a.            Volatilization of elements

                             b.            Combination or adsorption of elements with ash constituent or the vessel.

                              c.            Incomplete extraction of the ash, such difficulties can usually be avoided.

3.2.3.2 WET/ACID DIGESTION

            All acid procedure makes use of oxidizing agents to break down the organic matters.

The method has some advantages when compared with dry ashing as no volatilization loss occurs. The nutrient elements can be determined in one digest solution, but can not be used for some very hard materials as incomplete digestion may result. Various chemicals such as nitric acid, percholoric and sulphuric acid can be used in the determination of lead, iron, copper, nickel, cadmium and other heavy metals. The use of hydrochloric acid was employed in this project because the digestion is very fast though it is dangerous in the sense that explosion may occur if care is not taken.

The solution after digestion will then be made up to the mark in the volumetric flask to move the sample solution. (Milacic and kralj, 2003).

3.2.4 THEORY OF ANALYSIS

          The analysis of trace element present in the sample solution can be carried out by the use of classical or instrumental method.  However the instrumental method of analysis is more reliable than classical method. The instrumental method involves the use of instruments like the flame photometer, Atomic absorption spectrophotometer (AAS) (Agrawal, 2003).

3.2.5 SAMPLE PREPARATION

          The vegetables were collected from three (3) different farms in Kabala west area of Kaduna and were brought into the laboratory. The leaves were plucked from the stem and were properly washed with de-ionized water; the leaves were than dried at room temperature until it was ready for grinding.

          The dried leaves were then pounded with the crucible to fine powder the different leaf samples were then labeled into different small crucibles for identification

3.2.6  DIGESTION PROCEDURE

The glass wares were washed and cleaned properly and were rinsed with distilled water. Five (5) grams of each sample were weighed into a beaker, 10ml of each of the acid (Nitric and perchloric acid) with one ml of sulphuric acid were mixed into separate beaker, the acid mixtures were added to the sample in the beaker and were stirred continuously for few minutes, and 5ml of distilled water was added and was stirred again. The solution was filtered into a volumetric flask and was poured into a labeled sample bottle; the volumetric flask was rinsed with distilled water into the sample which was made up to the mark.

The same procedure was repeated for the rest of the samples and was then taken for analysis of the heavy metals using PG-990 atomic absorption spectrophotometer (Obuobie et al., 2006).

3.2.7 ATOMIC ABSORPTION SPECTROPHOTOMETRY

3.2.7.1 PRINCIPLES OF ATOMIC ABSORPTION SPECTRODCOPY

          In atomic absorption analysis, the absorption of Light use of an instrument called Atomic absorption spectrophotometer (AAS), in this process, a flame system is generally employed to dissociate elements from their chemical bonds. The atoms absorb light at characteristic wavelength when present in their ground state. A mixture of air and acetylene produce a flame which is of a sufficient high temperature to ensure the presence of free atoms of most elements. The use of nitrous oxide in place of air result in a higher temperature and this is necessary for the estimation of certain elements. (Obuobie et al., 2006).

CHAPTER FOUR

4.0     RESULTS

          Table 1: Result for the analysis of heavy metals in mg/kg

Samples	Lead	Cadmium	Zinc
Fluted pumpkin	6.015 ± 0.011	1.585 ± 0.017	3.580 ± 0.034
Spinach	9.075 ± 0.009	1.515 ± 0.017	6.765 ± 0.025
Bitter-leaf	3.045 ± 0.011	1.365 ± 0.013	2.720 ± 0.053
Lettuce	2.130 ± 0.010	1.405 ± 0.020	ND
Cabbage	2.750 ± 0.010	1.735 ± 0.016	ND

          Key: ND – Not detected

         

4.1     PERMISSIBLE GUIDELINE FOR HEAVY METALS IN VEGETABLE

There are permissible guideline and levels of heavy metals in vegetable which is set by the food nutrition board and WHO (World Health Organization) and they are as follows:

Metals	Value mg/kg
Lead	0.3
Zinc		100
Cadmium		0.10

4.2     DISCUSSIONS

WHO (World Health Organization) standards and permissible levels for the metals of interest (Lead, Cadmium, and Zinc) are 0.3mg/kg, 0.10mg/kg and 100mg/kg respectively. The result of this project indicated that the analyzed metals; Lead (2.130-9.075mg/kg), Cadmium (1.365-1.735mg/kg) were present in all the samples except for Zinc (2.720-6.765mg/kg) which was not detected in lettuce and cabbage; the concentrations of heavy metals in vegetables differ from one sampling location to the other and vary from one specie of vegetable to the other. Among all the heavy metals analyzed, the concentration of Lead (9.075mg/kg) detected in spinach was the highest and that of Cadmium (1.365mg/kg) detected in bitter-leaf was the lowest in all samples analyzed. With the exception of Zinc the levels of Lead and Cadmium detected in most of all the samples analyzed in this project were higher than the stipulated permissible levels in food by FAO/WHO guidelines. Since the levels of Lead in all the vegetable samples were above the permissible level, continuous consumption of this vegetables can cause several health effects such as ; kidney damage, brain damage, rise in blood pressure, miscarriages and infertility. The concentration of Cadmium was also above the limit and can result in health effects such as lung problems which include pneumonitis and pulmonary edema, liver injury, convulsions etc.   

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CHAPTER FIVE

5.0     CONCLUSION AND RECOMMENDATIONS

5.1     CONCLUSION

This project has determined the various concentrations of the metals of interest, it has shown that out of the three metals analyzed only Zinc (2.720-6.765 mg/kg) did not exceed the permissible limit of (100 mg/kg) and both Lead (2.130-9.075mg/kg) and Cadmium (1.365-1.735 mg/kg) exceeded the permissible limit of (0.3 mg/kg) and (0.10 mg/kg) set by FAO/WHO in all the sample analyzed, it is therefore concluded that vegetable grown in this area (Kabala west) and irrigated with polluted water is not safe for consumption.

5.2     RECOMMENDATIONS

·                    This project work stresses the responsibility of the authorities in Kaduna state and the country at large to make sure that foods are processed in relevant areas and of good quality. Based on the data obtained from this project, farmers should be sensitized by the government and NGOs (Non- Governmental Organizations) on the ill-effects of heavy metals on human health and also on the need to minimize the use of polluted water for irrigation.

·                    Sequel to this project, other researches should be made to ascertain the concentrations of other heavy metals such Arsenic, Nickel, Cobalt etc.

·                    Other vegetable samples can also be researched upon to ascertain the concentration of heavy metals in them.

·                    Measures have to be taken in other not to heavily pollute the irrigation water with heavy metals to protect the safety of vegetable consumers and the environment.

·                    It is very important to conduct a subsequent study to access the levels of toxic metals for the vegetables that are grown in different farms in Kaduna State, Findings from such works in conjunction with the findings in this project will help persuade policy makers on the need to identify suitable and non-suitable area for vegetable production in the state.

REFERENCES

 Agrawal, M., (2003). Enhancing food chain integrity: quality assurance           mechanism for air pollution impacts on fruit and vegetable system. Final technical report for department of international development, UK, P. 7530.

Amoah, P., (2008). Waste water irrigated vegetable production: contamination pathyway for health risk reduction in Accra, Kumasi and Temale-Ghana. Ph.D. Thesis, kwame nkrumah university of science and technology, kumasi, Ghana, PP: 74-75.

Angelova, V., R. Ivanov, V.Delibaltova and K. Cvanov, (2004) bio-accumulation and distribution of heavy metals in fibre crops (flax, cotton and hemp). Ind. Crops prod., 19:197-205.

Ayers, R.S. and D.W. Westcot, (2001) water quality for agriculture, irrigation and drainage paper 29 Rev.1, food and agriculture organization of the United Nations (FA O), Rome.

Bigdeli, M. and M. Seilsepour, (2008). Investigation of metals accumulation in some vegetables irrigated with waste water in shahre rey-Iran and toxicological implications. Am. Euras. J. Agric. Env. Sci., 4(1).

Haiyan, W. and A.O. Stuanes, (2003). Heavy metal pollution in air-water-soil-plant. water air soil pollut., 147:79-107.

Jarup, L., (2003). Hazards of heavy metal contamination. Br. Med. Bull., 68:167-182.

Jassir, M.s., Shaker, A., and Khaliq, M., (2005). Deposition of heavy metals on green leafy vegetables sold on road sides of Riyadh city, Saudi Arabia. Bull. Environ. contam. toxicol.,75:1020-1027.

Kabata-pendias, A., and Pendias, H., (1999). Trace Elements in soils and plants. Crc press.

Khillare, P.S., Balachandran, S., and Meena, B.R., (2004) Spatial and Temporal variation of heavy metals in atmospheric aerosols of Delhi. Environ. Monit. Assess., 90:1-21.

Laura, DK., and Susan H., (2009). Early kidney damage in population exposed to cadmium and other heavy metals. Environ. Health perspect, 117(2): 181-184.

Milacic, R., and Kralj, B., (2003). Determination of Zn, Cn, Cd, Pb, Ni and Cr in some slovenian food stuffs. Eur. Food res. technol, 217:211-214.

Mohsen, B., and salisu, S., (2008). Investigation of metals accumulation in some vegetables irrigated with waste water in shahre rey-Iran and toxicological implications. American-eurasian J. Agric. Environ. sci., 4:86-92.

Obuobie, E., B. Keraita, G.Danso, P. Amoah, 0.0., L. Raschid-sally and P.Drechsel., (2006). irrigation urban vegetable production in Ghana: characteristics, Benefits and Risks. IWMI-RUAF-CPWF, Accra, IWMI, Ghana, pp:150.

Pendias, A.K., and H. John, (2002). elements of group viii. in: Trace element in soil and plants. CRC Press, Boca, Raton, PP:271-276.

Pescod, M.D., (1999). Waste water treatment and use in agriculture FAO irrigation  and drainage paper no.47, food and agriculture organization of the united nations, Rome, Italy pp:125-156.

Pilot, CH., and Dragan, P.Y, (2006). Chemical carcinogenesis. toxicology International edition, Fifth Ed, PP:201-260.

Radwan, M.A., and Salama, A.K., (2006). Market basket survey for some heavy metals in Egyptian fruits and vegetables. Food chem. Toxicol., 44:1273-1278.  

Thompson, H.C., and Kelly, W.C., (2003). Heavy metals in soil, vegetables              and fruits in endemic upper Gastrointestinal cancer region of Turkey. Environ. Toxicol.pharmacol., 13: 175-179

Torobian, A., and Mahjoun, M., (2002). Heavy metals uptake by vegetable crops irrigated with waste water in south Tehran J. Environ. Study, P. 16

WHO, (2006). Guidelines for the safe use of waste water, excetera and grey water: Waste water use in agriculture (volume 2). Geneva, WHO, 2:219.

Yargholi, B., and Azimi, A.,(2008) Investigation of cadmium absorbtion and accumulation in different parts of some vegetables. J. Agric. Environ. Sci., 3:357-364

Zurera, G., Moreno, R., Salmeron, J., and Pozo, R., (1999). Heavy metals uptake from greenhouse border soils for edible vegetables. J. Sci. Food and Agric., 49:307-314.